Voice over Long-Term Evolution (VoLTE), a standard for high-speed wireless communication for user equipment (UE) such as mobile phones and data terminals, is based on the IP Multimedia Subsystem (IMS) network, with specific profiles for control and media planes of voice service on LTE. Voice service is delivered as data flows within the LTE data bearer, which provides three times more voice and data capacity than 3G UMTS, up to six times more than 2G GSM, and frees up bandwidth because VoLTE packet headers are smaller than those of unoptimized VoIP/LTE.
During a VoLTE call, an originating subscriber seeks to establish a call with a terminating subscriber. The terminating subscriber, however, may not answer the call. In response, a Telephony Application Server (TAS) can initiate a call forwarding procedure, which includes call forward not reachable (CFNR); call forwarding unconditional (CFU); and call forwarding busy (CFB). A call forwarding procedure uses a subscriber's profile information to retrieve a voicemail pilot number from the voicemail server. The pilot number is an SS7 number that designates a directory number to access the subscriber's voicemail messages. Each pilot number can belong to a different voicemail messaging system.
An analogous process occurs for voicemail message retrieval. For example, a subscriber can dial a number on a UE to access voicemail messages. During a procedure to deposit/retrieve a voicemail message, the TAS issues an Intelligent Network Application Protocol (INAP) query to obtain the subscriber's pilot number from the voicemail server. Based on the INAP response, the TAS sends an INVITE message to request that an endpoint join a SIP session to deposit/retrieve the voicemail message to/from a voicemail server.
The drawings have not necessarily been drawn to scale. Similarly, some components and/or operations may be separated into different blocks or combined into a single block for the purposes of discussion of some of the embodiments of the present technology. Moreover, while the technology is amenable to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and are described in detail below. The intention, however, is not to limit the technology to the particular embodiments described herein. On the contrary, the technology is intended to cover all modifications, equivalents, and alternatives falling within the scope of the technology as defined by the appended claims.